In fabricating microelectronic semiconductor devices and the like on a wafer substrate or chip, e.g., of silicon, to form an integrated circuit (IC), etc., various metal layers and insulation layers are deposited in selective sequence. To maximize integration of device components in the available substrate area to fit more components in the same area, increased IC miniaturization is utilized. Reduced pitch dimensions are needed for denser packing of components per present day very large scale integration (VLSI), e.g., at sub-micron (below 1 micron, i.e., 1,000 nanometer or 10,000 angstrom) dimensions.
One type of wet chemical process used in the IC fabrication of a semiconductor wafer concerns the chemical mechanical polishing (CMP) of a surface of the wafer against a polishing pad during relative periodic movement therebetween, such as with a caustic slurry containing finely divided abrasive particles, e.g., colloidal silica in an aqueous potassium hydroxide (KOH) solution, as the polishing liquid. This removes, i.e., by chemical etching and mechanical abrasion, a thin layer of material, e.g., of 1 micron or less thickness, so as to planarize a top surface of the wafer. Close control of the slurry flow rate, temperature and pH are necessary to attain in a reproducible manner a uniform removal rate per the CMP operation.
The conventional CMP process involves introducing the slurry from a stationary overlying tube dropwise onto a polishing pad of a rotating table (platen) which rotates about a stationary platen axis and against which the wafer, which is carried by a retaining ring, makes frictional contact while the wafer and ring rotate and oscillate relative to the platen. The wafer is positioned in a medial aperture of the ring such that the ring also makes frictional contact with the polishing pad. As the position of the wafer relative to the platen varies during wafer rotation and oscillation, the slurry dispensing tube is always spaced a minimum clearance distance from the wafer.
Consequently, different portions of the wafer necessarily encounter dispensed slurry droplets having different thermal histories. This depends on the continuously varying distance between the relative position of rotation and oscillation of the wafer, and in particular of its leading and trailing edges during oscillation, and the position of the centrifugally outwardly travelling slurry droplets dispensed onto the rotating platen from the stationary tube. As a result, the operating temperature at the local polishing site of the wafer is non-uniform, leading to non-uniformity of the CMP operation.
Also, some of the slurry on the polishing pad is pushed off the platen by the retaining ring which surrounds the wafer, inasmuch as the ring is also in frictional contact with the pad and in some cases is pressed under positive mechanical pressure thereagainst. This loss of slurry constitutes wastage which increases operating costs. By its inherent wafer-captively surrounding arrangement, the retaining ring also impedes flow of slurry to the central area of the wafer surface being polished. This causes poor center-to-edge uniformity, further detracting from the uniformity of the CMP operation.
Where the process requires heating of the slurry, such as in the case of polysilicon CMP, then a separate heating module, which occupies expensive floor space (module footprint), must be provided to supply heated slurry to the tube for dispensing.
The above prior art drawbacks cause adverse variation in the local removal rate of wafer material from different parts of the wafer due to variation in the amount and temperature of the slurry coming into contact with the wafer surface being polished. This diminishes the degree of within-wafer uniformity. Also, slurry wastage increases its consumption rate and cost.
It is desirable to have a system, including a method and an apparatus, permitting CMP operations to be performed on a semiconductor wafer under reproducible uniform conditions of polishing liquid temperature, polishing liquid dispensing flow rate, and supplying of polishing liquid locally to all portions of the wafer regardless of its relative position of movement with respect to the platen polishing pad, and optionally also under reproducible uniform conditions of selective temperature adjustment of the polishing liquid in the vicinity of the wafer.